TS blade gets harmonic chatter and kerf widens?

[Jacob Reverb]

Hey, all,

Getting a strange phenomenon on my table saw, wondering if anyone else has seen this and might be able to suggest possible causes.

Several years back, I bought several 10" Irwin Marathon carbide 24T ripping blades (package labeled #14233, blade labeled #24233) at Lowe's because they were so cheap (I'm a sucker for bargains) and because I often use TS for rough/construction grade jobs.



Anyway, when I use these blades for ripping 1" SYP or even 7/16" plywood, the blade seems to suddenly develop a wobble or chatter, almost like a percussionist's cymbal, and it makes a lot of noise when this happens (a growly SHHHHH sound like a cymbal makes), and the kerf widens by probably 50%.

This wobble or shimmy or whatever it is seems to be tied to both workpiece hardness and feed rate. Sometimes it does it when going through a knot, and sometimes it does it for no apparent reason. It seems almost like a harmonic vibration -- that somehow the blade might flex and start to get some runout in it, which then worsens due to harmonic feedback. If you stop feeding, the kerf width returns to normal and noise ceases. There's no burning of the wood associated with this when it happens -- just the sudden "cymbal" noise and widening of the kerf.

It does this with a fairly sharp used blade, and I just tested a brand-new specimen of the same make/model blade, and it does the same thing. FWIW, I have height set such that carbide teeth just clear the top surface of the workpiece, and the trunnion height and angle nuts are both tight. Also, fence is parallel to blade (or skewed maybe 1/32" - 1/64" away from blade at rear), the arbor bearings are new, and arbor runout/parallelism to miter slot seems to be negligible (1-2 mils). Arbor flange is smooth, arbor washer is flat, and the saw doesn't do this with other blades.

Has anyone else seen this and does anyone have any idea why it might happen? Unfortunately, I bought several of these blades 10 or 15 years ago because they were so cheap, and now I'm thinking I might have bought defective blades and there's nothing I can do with them, since I probably can't return them anymore...

Thanks in advance for any clues...

Jacob.

[Joe Jensen]

Might be why they were so cheap? Probably the plate was not properly tensioned. I'm sure someone who sharpens blades can explain better.

Here is a quote from the web.

1. TENSION - This seems to be the mystery word used in saw hammering. It is actually a very simple function in most carbide saws. Tension is very important in large diameter saws, but in small saws the amount required is so little that in most cases it is checked merely to judge the uniformity of the saw to correct for loose or tight areas. Tension in a saw has to do with the equalizing of strain on the saw caused from the centrifugal force stretching the rim. When the rim stretches it pulls on the body of the saw. This is why the body must be stretched slightly so the rim has this stretch to compensate for. Thermal expansion of the rim or hub and cutting strain need to be compensated for by tension. If the saw does not bend with a uniform curve when broken at the center line, the tension is not uniform and the saw will have a high speed wobble. The amount of tension needed in small saws is not too great; thin saws do require slightly more tension than heavy ones.

[Alan Schwabacher]

It does sound like a resonance, and related to the blade price. Since your cut depth is small, you should be able to fix it with blade stabilizers.

[glenn bradley]

It does sound like a resonance, and related to the blade price. Since your cut depth is small, you should be able to fix it with blade stabilizers.

Yes, this for TK blades. For your construction jobs I wouldn't worry about it. I found thin kerf blade flutter to be minimized on a well aligned saw. I was able to stop using my stabilizers once I spent a little time on my machine setup. Sometimes, machine, speed and blade will combine to work against you.

[Frank Pratt]

Sometimes a bargain is no bargain at all. But they should be fine for ripping framing lumber.

[Jacob Reverb]

Thank you for the replies, fellas. TS is tuned (at least according to my measurements) better than it's ever been, so I'll try some blade stabilizers and report back.

[johnny means]

This happens with $300 14" blades on industrial sliders, too. Maybe not as often, but it happens. I try to use a freshly cleaned blade and blade lube when I'm making cuts that I know tend to get loud.

[Jamie Buxton]

Blades flutter more as they get dull. Misbehavior is an earlier indicator of dullness than feeling dull to your finger or looking dull.

[Jacob Reverb]

This happens with $300 14" blades on industrial sliders, too. Maybe not as often, but it happens. I try to use a freshly cleaned blade and blade lube when I'm making cuts that I know tend to get loud.

Interesting, thanks. Just spoke to a millwright friend who's worked on circular sawmills, who said the same thing. He seemed to think it's worse when cutting thin stuff where you're just using the edge of the blade and cutting more tangentially as opposed to having the blade up high on thicker material, where the teeth are cutting at a more square angle to the workpiece.

What do you use for blade lube on your 14" saw? I'm not familiar with that...

[Steve Rozmiarek]

This happens with $300 14" blades on industrial sliders, too. Maybe not as often, but it happens. I try to use a freshly cleaned blade and blade lube when I'm making cuts that I know tend to get loud.

I have an expensive ripping blade that I bought with my slider that I never use because of this very thing. It's factory sharp still, one of these days I'll toss it.

[Tim Bueler]

I had a CMT Glue Line Rip blade that did that right out of the box. I got a hold of the seller and they sent a replacement right away. The new blade runs flawlessly.

[Randy Heinemann]

I have used Freud blades on 10" saws for many years and have never had this happen, even with thin kerf blades. Although Freud blades are more expensive than the Irwin blades above, they are, by no means expensive blades. I have a Sawstop 10" saw with a Sawstop blade and no vibration in the 3 years I've owned it.

[Lee Schierer]

You don't mention which table saw you have. Those Irwin 10" blades are limited to 5900 rpm.

Per the Irwin website:
irwin.JPG

[Jacob Reverb]

Thanks, guys.
Lee, it's a Powermatic 64A that I bought new around 1998, and manual says it's 4500 rpm.
Randy, most of my blades are Freuds, too -- mostly full-kerf -- and never a problem with any of them.

[Bruce Wrenn]

If you have an infared temp probe, shoot the blade and see if it's getting hot. My bet is it's over heating, and then warping. I've had only one blade to ever do this, but it was a real surprise when it did. Had to make a new zero clearance insert for saw.